This invention relates to a circuit interrupter in which a movable contact is moved to open by an electromagnetic repulsive force resulting from a massive current irrespective of the interrupting operation by an automatic trip mechanism.
A conventional circuit interrupter to which the present invention pertains will be described in conjunction with FIGS. 1 to 6. FIG. 1 is a sectional side view of the conventional circuit interrupter, FIG. 2 is a partial enlarged sectional view of FIG. 1 showing the ON position, FIG. 3 is a view similar to FIG. 2, but illustrating the OFF position, FIG. 4 is a view similar to FIG. 2, but illustrating the TRIP position, FIG. 5 is a view similar to FIG. 2, but illustrating the electromagnetically operated position, and FIG. 6 is a view similar to FIG. 2. but illustrating the position at which the first contact arm is being reset.
In these figures, the circuit interrupter comprises an electrically insulating housing 1 composed of a base 1a and a cover 1b. A stationary source side conductor 2 is mounted on the base 1a and has a stationary contact 3 secured thereon. An automatic trip unit 4 is mounted in the housing 1, and a stationary load side conductor 4 is electrically connected to the automatic trip unit 4. A movable contact 6 is secured to a movable member 7 which is electrically connected to the automatic trip unit 4 through a flexible conductor 8 and a connector 9. The movable member 7 is supported by a contact arm assembly 10 comprising a first contact arm 10a connected to an operating mechanism 20 which will be described in more detail later, and a second contact arm 10b on which the movable member 7 is pivotally supported by a first pin 11. The first contact arm 10a of each pole unit is also connected to a cross bar 13 for the simultaneous movement of the pole units. The first contact arm 10a and the second contact arm 10b are pivotally supported independently within the housing by a pivot pin 12. The first contact arm 10a has formed therein a first guide hole 14 extending substantially in the direction of the movement of the contact arm 10a. The second contact arm 10b has formed therein a second elongated guide hole 15 extending in the direction of extension of the arm 10b. A pin 16 extends through the first and the second guide holes 14 and 15 to limit the relative pivotal movement between the first and the second contact arms 10a and 10b. The pin 16 is biased toward the free end of the contact arm 10b by a tension spring mounted between the pin 16 and the pin 11 pivotally connecting the movable member 7 to the second contact arm 10b. In order to provide a contact biasing force between the movable and the stationary contacts 6 and 3, a contact pressure spring 18 is disposed between the movable member 7 and the second contact arm 10b. An operating handle 19 is connected to an operating mechanism 20 comprising a releasable cradle 20a having a stop pin 21 and a pair of toggle links 20b and 20c connected between the cradle 20a and the first contact arm 10a by pivot pins 22a and 22b. As is well known, an arc extinguisher 23 is disposed in order to extinguish the arc generated between the separated contacts when they are separated.
When the circuit interrupter is in the ON position shown in FIGS. 1 and 2, an electric current flows from the source side stationary conductor 2 to the load side stationary conductor 5 through the stationary contact 3, the movable contact 6, the movable member 7, the flexible conductor 8, the connector 9 and the automatic trip unit in the named order. When the operating handle 19 is moved into the OFF position as shown by an arrow 24 of FIG. 2, the contact arm assembly 10 is lifted by the operating mechanism 20 so that the movable contact 6 together with the movable member 7 is moved away from the stationary contact 3 as shown in FIG. 3 to open the contacts 3 and 6. At this time, since the second pin 16 is positioned in the recessed portion 14a of the guide hole 14 due to the biasing function of the tension spring 17, the second contact arm 10b is rotated about the pivot pin 12 in the opening direction by the operating mechanism 20 together with the first contact arm 10a until it abuts against the stopper pin 21.
In the ON position shown in FIGS. 1 and 2, when an overload current flows through the circuit interrupter, the automatic trip unit 4 is actuated to release the cradle 20a of the operating mechanism 20 to allow it to rotate in the direction of an arrow 25 of FIG. 2. Then, the toggle links 20b and 20c of the operating mechanism 20 rotate the contact arm assembly 10 in the clockwise direction in the figure to separate the movable contact 6 from the stationary contact 3, thereby interrupting the overload current. This is the socalled tripped position. During this operation, since the second pin 16 is positioned within the recessed portion 14a of the guide hole 14 due to action of the tension spring 17 similarly to the OFF position shown in FIG. 3, the second contact arm 10b is rotated clockwise about the pivot shaft 12 by the operating mechanism 20 together with the first contact arm 10a until it abuts against the stopper pin 21.
When a large current such as a short-circuit current flows through the circuit interrupter in the ON position shown in FIGS. 1 and 2, an electromagnetic repulsive force generated between the stationary conductor 2 and the movable member 7 causes the movable member 7 to immediately separate from the stationary conductor 2 as shown in FIG. 5. At this time, since the operating mechanism 20 does not allow the first contact arm 10a to be actuated because it has not yet been actuated itself, the second contact arm 10b rotates clockwise as shown by an arrow 26 about the shaft 12 by moving the second pin 16 against the spring force of the tension spring 17 from the recessed portion 14a along the guide hole 14 until it abuts against the end portion 14b of the guide hole 14. An electromagnetic repulsive force is generated very quickly upon the occurence of a short-circuit current and therefore the contact separation is achieved before the automatic try unit 4 is actuated, providing a high current limiting capability.
Immediately after the electromagnetic repulsive separation is achieved, the automatic trip unit 4 trips and rotates the first contact arm 10a to return the second pin 16 into the recessed portion 14a of the guide hole 14 after it has passed the position shown in FIG. 6 to take up the tripped position shown in FIG. 4. This is called the resetting of the contact arm assembly 10. At this time, the second pin 16 is moved along the pin sliding surface 15a of the elongated hole 15 while being biased by the tension spring 17 against the pin sliding surface 14c of the guide hole 14.
With the conventional circuit interrupter as above described, the angle .theta..sub.1 defined between the pin sliding surface 15a of the elongated hole 15 along which the second pin 16 slides and the pin sliding surface 14c of the guide hole 14 is smaller than 90.degree., the resetting force (upward) of the first contact arm 10a causes a force that presses the second pin 16 downward against the pin sliding surface 15a of the elongated hole 15. Then, the second pin 16 is sandwiched between the pin sliding surface 15a of the elongated hole 15 and the pin sliding surface 14c of the guide hole 14 by the above resetting force, making the movement of the first contact arm 10a poor and increasing the resetting load, to require a disadvantageously large mechanical force.